sd_bus_message_read_basic - Read a basic type from a message

sd_bus_message_read_basic() reads a basic type from a message and advances the read position in the message. The set of basic types and their ascii codes passed in type are described in the D-BusSpecification[1]. If p is not NULL, it should contain a pointer to an appropriate object. For example, if type is 'y', the object passed in p should have type uint8_t*. If type is 's', the object passed in p should have type constchar**. Note that, if the basic type is a pointer (e.g., constchar* in the case of a string), the pointer is only borrowed and the contents must be copied if they are to be used after the end of the message's lifetime. Similarly, during the lifetime of such a pointer, the message must not be modified. If type is 'h' (UNIX file descriptor), the descriptor is not duplicated by this call and the returned descriptor remains in possession of the message object, and needs to be duplicated by the caller in order to keep an open reference to it after the message object is freed (for example by calling "fcntl(fd, FD_DUPFD_CLOEXEC, 3)"). See the table below for a complete list of allowed types. Table1.Itemtypespecifiers ┌───────────┬─────────────────────────┬────────────────────────┬────────────────────────┐ │ Specifier │ Constant │ Description │ ExpectedCType │ ├───────────┼─────────────────────────┼────────────────────────┼────────────────────────┤ │ "y" │ SD_BUS_TYPE_BYTE │ 8-bit unsigned integer │ uint8_t* │ ├───────────┼─────────────────────────┼────────────────────────┼────────────────────────┤ │ "b" │ SD_BUS_TYPE_BOOLEAN │ boolean │ int* (NB: not bool*) │ ├───────────┼─────────────────────────┼────────────────────────┼────────────────────────┤ │ "n" │ SD_BUS_TYPE_INT16 │ 16-bit signed integer │ int16_t* │ ├───────────┼─────────────────────────┼────────────────────────┼────────────────────────┤ │ "q" │ SD_BUS_TYPE_UINT16 │ 16-bit unsigned │ uint16_t* │ │ │ │ integer │ │ ├───────────┼─────────────────────────┼────────────────────────┼────────────────────────┤ │ "i" │ SD_BUS_TYPE_INT32 │ 32-bit signed integer │ int32_t* │ ├───────────┼─────────────────────────┼────────────────────────┼────────────────────────┤ │ "u" │ SD_BUS_TYPE_UINT32 │ 32-bit unsigned │ uint32_t* │ │ │ │ integer │ │ ├───────────┼─────────────────────────┼────────────────────────┼────────────────────────┤ │ "x" │ SD_BUS_TYPE_INT64 │ 64-bit signed integer │ int64_t* │ ├───────────┼─────────────────────────┼────────────────────────┼────────────────────────┤ │ "t" │ SD_BUS_TYPE_UINT64 │ 64-bit unsigned │ uint64_t* │ │ │ │ integer │ │ ├───────────┼─────────────────────────┼────────────────────────┼────────────────────────┤ │ "d" │ SD_BUS_TYPE_DOUBLE │ IEEE 754 double │ double* │ │ │ │ precision │ │ │ │ │ floating-point │ │ ├───────────┼─────────────────────────┼────────────────────────┼────────────────────────┤ │ "s" │ SD_BUS_TYPE_STRING │ UTF-8 string │ constchar** │ ├───────────┼─────────────────────────┼────────────────────────┼────────────────────────┤ │ "o" │ SD_BUS_TYPE_OBJECT_PATH │ D-Bus object path │ constchar** │ │ │ │ string │ │ ├───────────┼─────────────────────────┼────────────────────────┼────────────────────────┤ │ "g" │ SD_BUS_TYPE_SIGNATURE │ D-Bus signature string │ constchar** │ ├───────────┼─────────────────────────┼────────────────────────┼────────────────────────┤ │ "h" │ SD_BUS_TYPE_UNIX_FD │ UNIX file descriptor │ int* │ └───────────┴─────────────────────────┴────────────────────────┴────────────────────────┘ If there is no object of the specified type at the current position in the message, an error is returned.

sd_bus_message_read_basic() was added in version 221.

sd_bus_message_read_basic - Read a basic type from a message

1. D-Bus Specification https://dbus.freedesktop.org/doc/dbus-specification.html systemd 257.7 SD_BUS_MESSAGE_READ_BASIC(3)

On success, sd_bus_message_read_basic() returns a positive integer. If the end of the currently opened array has been reached, it returns 0. On failure, it returns a negative errno-style error code. Errors Returned errors may indicate the following problems: -EINVAL Specified type string is invalid or the message parameter is NULL. -ENXIO The message does not contain the specified type at current position. -EBADMSG The message cannot be parsed.

systemd(1), sd-bus(3), sd_bus_message_append_basic(3), sd_bus_message_skip(3), sd_bus_message_read(3)